The present invention relates to voltage responsive switches and more particularly to voltage responsive switches characterized by an irreversible resistance change from a high resistance to a low resistance upon the application of a voltage greater than the threshold voltage of the switch.
Voltage responsive switches are utilized in a wide variety of electrical and electronic devices. For example, such switches are utilized in providing voltage protection to delicate instruments, such as meters, or in sequentially fired flash lamps. In this latter application, it is imperative that the voltage responsive switch exhibit an irreversible change in resistance, preferably from a high resistance state to a low resistance state, to insure reliable sequential flash operation. Since the use of sequential flash lamps occurs in uncontrollable conditions of high humidity, high temperature, and frequently in the presence of high electromagnetic radiation fields, it is imperative that such switches do not exhibit a reversible resistance change. For example, Sliva et al describe in the Journal of Noncrystalline Solids, 2(1970) 316-333, the bistable switching and memory characteristics of a variety of amorphous, organic, and polycrystalline materials useful in bistable switching devices. While such devices may be quite useful for their intended applications, their use in a sequentially operated flash lamp device is unsatisfactory because the bistable resistance characteristic can be altered by the presence of stray electromagnetic fields, for example.
Accordingly, it is an object of this invention to provide an irreversible voltage sensitive switch characterized by a high resistance state of greater than a megohm and a low resistance state of less than approximately 100 ohms. Briefly, the present switches can be prepared by mixing substantially pure grade copper powder of approximately 99.99% purity with copper oxide (Cu.sub.2 O) powder, adding an organic binder to the copper-copper oxide mixture and applying the resulting mixture or slurry to a pair of spaced electrodes. As will be described more fully below, the ratios of the copper-copper oxide powders and the spacing of the electrodes determines the threshold voltage at which the irreversible voltage sensitive switch changes from a high resistance to a low resistance.